Coatings from chemical vapor deposition, herein sometimes referred to as CVD, are used extensively in applications requiring resistance to wear, erosion, and corrosion over a wide range of temperatures. More often than not, the purpose of the coating is multifunctional. An example is the coating for a turbine parts, such as blades and vanes, to provide protection against wear and erosion of a corrosive environment at high temperature as well as protection against erosion by sand and other foreign particles. Aluminum is often the coating material chosen to protect turbine hardware involving the formation of aluminum oxide (Al.sub.2 O.sub.3) and metal-aluminum oxide layers.
Copending and commonly assigned U.S. application, "Low Temperature Chemical Vapor Deposition Method for Cleaning Substrate and Depositing Protective Coating," Ser. No. 08/315,807 filed Sep. 30, 1994, teaches a method to deposit aluminum coatings on turbine blades. Another copending and commonly assigned U.S. application, "Method for Low Temperature Chemical Vapor Deposition of Aluminides Containing Easily Oxidized Metals," Ser. No. 08/315,805 filed Sep. 30, 1994, discloses depositing metal oxides with an excess of aluminum. The metal oxides are subsequently reduced by aluminum to form aluminum coatings containing small amounts of metal.
In addition to using aluminum as a protective coating, it has been found that small amounts of platinum in the aluminum coating produce superior passivating films upon oxidation. The stability of the films further protect substrate metals from high temperature corrosion. Although platinum can be plasma sprayed or evaporated, it is not easily deposited by other physical vapor deposition methods.
It would be advantageous to have a method to co-deposit platinum with aluminum by low temperature chemical vapor deposition. Low temperature chemical vapor deposition allows uniform deposition of the coating within internal cooling passages of turbine hardware at temperatures which are not detrimental to the mechanical strength of the substrate material.
It would also be advantageous to have a method to form aluminide coatings that contain small amounts of platinum.